Stft+ltft != 0

[assa 98gsx]

This is kinda a newbie question. For ppl who tune with their pocketloggers, how do you tune the LO-THR points with the STFT and LTFT. When I adjust the LO points, the STFT never stays the same(I know it varies with the 02) and the STFT and LTFT never adds up to be zero. Do I just need to make the LTFT to be 0% or do I have to add them up and make them to 0%. My mods are big16G, FMIC, 550cc, 190fp, 3" exhaust, safcii, and datalogger.

Please teach me, thanks.

 

[ChicagoGSX]

http://home.comcast.net/~tarryo/kyle/tuning.html

2g's only have 2 fuel trims, a long term fuel trim (LTFT) and a short term fuel trim (STFT). The STFT varies with the O2 sensor, an the LTFT goes for every rpm range. Since the STFT directly effects the LTFT, then you can just add the two together, and tune from there. For example, if the LTFT is +20%, and the STFT is -5%, you are at approximately +15%.

You can also do this addition trick on a 1g with a TMO/Pocketlogger type setup.

Whew, that was exciting, but I think I covered it all. Now, on to the tuning. Set up your logger to display RPM, Airflow, and all the fuel trims your car has. Start the car and let it fully warm up. Leave it at idle, and we will begin to tune the low throttle table in the SAFC.

Now, look at the low fuel trim (2g's only have the LTFT). If it is positive, add a few percent on the SAFC at the 1000 rpm point. This is not an exact science, but usually for about every 3-5% on the logger, you need 1% on the SAFC. After adding or subtracting a few percent, let the car idle for a few minutes, and watch the fuel trims change. This may take a while, especially in a 1g, so just wait.

When this is done, free rev to 1500 rpm and hold it there. Do the same thing, it will probably still be on the low fuel trim.

Continue to do this at 2k, and 3k rpm. After you are done and are fairly confident they are close, take the car for a drive and see if they change. Try to get the fuel trims close to 100%, plus or minus 10% Keep in mind that in a 1g, a perfect fuel trim is 100%, but in a 2g it's 0%.. That means that in a 2g, if the fuel trim is negative, you have to lean it out a bit, and if it's positive, you have to richen it up.

Once they are within 5 or 10%, and they have stayed that way for a drive, you can carry the numbers across up to 7k rpm. So, if you have +5% at 3k and 4k rpm, use +5% at 4.5k, 5k, 6k, and 7k. Then, you will also want to use +5% on your high throttle table, all the way across, until we begin to tune it in the next issue.

 

[kpt4321]

Holy crap. That's almost exactly what I would have said.




....Kyle T.